EXPERIMENTAL-STUDY OF SURFACE SEGREGATION AND WETTING IN FILMS OF A PARTIALLY MISCIBLE POLYMER BLEND

We have studied composition-depth profiles in thin films of blends of deuterated polystyrene and poly(cr-methyl styrene) using neutron refle ctometry and He-3 nuclear reaction analysis. Some of the neutron refle ctometry data are analyzed using a maximum entropy technique with Baye sian probability. One blend is miscible for all compositions at the te mperature studied (180 degrees C), and we are able to obtain a bare su rface energy difference between the two polymers from the equilibrium surface profile. The other blend that is studied is partially miscible , and here we have compared the approach to wetting in this blend with a simple model based on mean field theory. For quenches deeper into t he metastable region of the phase diagram, the simple model fails due to, we believe, a competition between wetting and bulk nucleation and growth.